The present invention relates to skin whitening compositions that contain an extract of black cohosh. The extract can be obtained by exposing the black cohosh, or a portion thereof, to a single solvent or by sequentially exposing the black cohosh to two or more solvents of varying solvent strengths. The compositions are suitable for external use through topical application. The present invention further relates to the cosmetic use of such compositions, and a method of suppressing melanogenesis.
Skin color is primarily determined by the amount of melanin in the skin. Melanin is a brown-black pigment present in the skin. Due to the dark color of the pigment, lower amounts of melanin result in lighter skin color while higher amounts result in darker skin color. Melanin is formed by the oxidation of the amino acid tyrosine to dihydroxyphenalanine in melanocytes. This reaction is catalyzed by the enzyme tyrosinase.
As a result of this pivotal role of tyrosinase in melanin formation, efforts to develop effective skin whitening compositions have focused on agents that inhibit the function and activity of tyrosinase. For example, compositions have been proposed that include a variety of known tyrosinase inhibitors, such as hydroquinone, vitamin C and its derivatives, kojic acid, arbutin, glutathione, cysteine, and mulberry extract, among others. Compositions including these agents achieve a skin whitening effect through inhibition of the catalysis of the tyrosine oxidation reaction by tyrosinase.
The present inventors have discovered that certain extracts of black cohosh effectively suppress the formation of melanin, melanogenesis, despite the fact that the extracts show little to no inhibition of tyrosinase activity. This result is surprising and unexpected considering the pivotal role of tyrosinase in melanogenesis and the focus of development efforts in the art to inhibit this enzyme.